Friday, March 30, 2012

Gemstone of the Week: Sillimanite

(Sillimanite sample from Cercagems.com)

Images of Sillimanite

Sillimanite is a closely related gem to Kyanite, in fact, it is one of the three polymorphs of Al2SiO5  (chemical composition aluminum silicate oxygen), the other two are Kyanite and Andalusite.  Most often it is found as colourless to white in colour, but it can also be pale yellow to brown, pale blue, green, or violet. Sillimanite occurs as either long, slender glassy crystals or as blocky and poorly terminate prisms. It is a highly pleochroic (it shoes different colours at different angles) and has yellow-green, dark green, and blue within the same stone depending on the angle. Sillimanite is often found with Corundum, Kyanite, and Cordierite.  Sillimanite is found in Scotland, Vltava, the Czech Republic, India, Canada, and the U.S.

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